The September through November months are expected to feature near to above-average temperatures across a large swath of the United States, according to an updated fall temperature outlook by The Weather Company, an IBM Business. The East Coast will likely see temperatures the farthest above average.

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Below-average temperatures will prevail across the Pacific Northwest into the northern Plains, however, said Dr. Todd Crawford, chief meteorologist with The Weather Company.

According to Crawford, the September forecast is now warmer across the eastern half of the U.S. and cooler across much of the West. These substantially warmer changes to the forecast in the East and slightly cooler changes in the West were made because of the weather pattern that is expected to take shape during the first half of September.

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This pattern favors a trough (dip in the jet stream) across the western U.S. that will allow cool air to drop down from Canada, while a large ridge of high pressure (bulge in the jet stream) dominates the East and allows the warmth to build.

The real wild card in September is tropical activity which could have an influence on temperature patterns. This is something that cannot be predicted very far in advance.

Much of the Northwest, including Washington and Oregon, will see below-average temperatures during September.

October-November Outlook

According to Dr. Crawford, a weak La Niña (cooler-than-average waters off the west coast of South America) could be in play through the fall and winter months, although the horizontal extent of those cooler-than-average waters is expected to be smaller than usual. At the same time, warmer-than-average water temperatures will prevail across much of the North Pacific.

One fall and winter season that featured similar conditions was 1995-96, so the updated fall temperature outlook was based on what occurred then. That season was particularly cold during late fall and into winter, but Dr. Crawford indicated that there was considerable atmospheric blocking in the higher latitudes (strong high-pressure ridges).

This was at least partially a result of low sunspot activity, also known as a solar minimum. Since this won't be the case during the upcoming months, the current temperature forecast was tempered from what occurred in the 1995-96 season.

October

Northeast: Warmer than average
Southeast: Slightly warmer than average
North Central: Cooler than average Plains; near to slightly warmer than average in the upper Midwest
South Central: Slightly warmer than average
Northwest: Cooler than average
Southwest: Near to slightly warmer than average

November

Northeast: Cooler than average
Southeast: Near to slightly warmer than average
North Central: Cooler than average
South Central: Warmer than average
Northwest: Cooler than average Washington to Montana, near to slightly above average elsewhere
Southwest: Near average

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